The growth of a normal cell or of a virus in its host cell involves a complex pattern of gene expression in which individual genes or groups of genes are activated or repressed at appropriate times during growth. Studies of the growth of bacterial cells and of bacteriophages have provided an important model system for the study of how gene expression is regulated. Those studies suggest that regulation of transcription - DNA dependent synthesis of messenger RNA - is of major importance in the control of gene expression. We propose to continue our studies of the steps involved in enzymatic transcription by E. coli RNA polymerase. Specific goals will be (1) Continution of studies on the individual steps involved in selective transcription. These will include a more detailed study of the specific interactions involved in promoter site selection and activation, kinetic studies on the chain initiation and elongation steps of the reaction and further development of specific assays for chain termination. (2) Studies on the intrinsic activity and specificity of E. coli RNA polymerase in cell extracts and the development of a new purification procedure for RNA polymerase holoenzyme.